1.2 Carboydrates

Question 1

What are monosaccharides? Give 3 common examples

Answer 1

● Monomers from which larger carbohydrates are made
● Glucose, fructose, galactose

Question 2

Describe the structure of α-glucose

Answer 2

Question 3

Describe the difference between the structure of α-glucose and β-glucose

Answer 3

● Isomers - same molecular formula but differently arranged atoms

● OH group is below carbon 1 in α-glucose but above carbon 1 in β-glucose

Question 4

What are disaccharides?

Answer 4

● Two monosaccharides joined together with a glycosidic bond

Question 5

How are disaccharides formed?

Answer 5

● Formed by a condensation reaction, releasing a water molecule

Question 6

What are the monosaccharides of maltose?

Answer 6

Glucose + glucose

Question 7

What are the monosaccharides of sucrose?

Answer 7

Glucose + fructose

Question 8

What are the monosaccharides of lactose?

Answer 8

Glucose + galactose

Question 9

Draw a diagram to show how two monosaccharides are joined together

Answer 9

Question 10

What are polysaccharides?

Answer 10

● Many monosaccharides joined together with glycosidic bonds

Question 11

How are polysaccharides formed?

Answer 11

● Formed by many condensation reactions, releasing many water molecules

Question 12

Describe the basic function of starch

Answer 12

Energy store in plant cells

Question 13

Describe the basic function of glycogen

Answer 13

Energy store in animal cells

Question 14

Describe the basic structure of starch

Answer 14

● Polysaccharide of α-glucose
● Some has 1,4-glycosidic bonds so is unbranched (amylose)
● Some has 1,4- and 1,6-glycosidic bonds so is branched (amylopectin)

Question 15

Describe the basic structure of glycogen

Answer 15

● Polysaccharide made of α-glucose
● 1,4- and 1,6-glycosidic bonds → branched

Question 16

Explain how the structure of starch relates to its function

Answer 16

● Helical → compact for storage in cell

● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane

● Insoluble in water → water potential of cell not affected (no osmotic effect)

Question 17

Explain how the structure of glucose relates to its function

Answer 17

● Branched → compact / fit more molecules in small area

● Branched → more ends for faster hydrolysis → release glucose for respiration to
make ATP for energy release

● Large, insoluble polysaccharide molecule → can’t leave cell / cross cell membrane

● Insoluble in water → water potential of cell not affected (no osmotic effect)

Question 18

Describe the basic function of cellulose

Answer 18

● Provides strength and structural support to plant / algal cell walls

Question 19

Describe the basic structure of cellulose

Answer 19

● Polysaccharide of β-glucose

● 1,4-glycosidic bonds so forms straight, unbranched chains

● Chains linked in parallel by hydrogen bonds, forming microfibrils

Question 20

Explain how the structure of cellulose relates to its function

Answer 20

● Every other β-glucose molecule is inverted in a
long, straight, unbranched chain

● Many hydrogen bonds link parallel strands
(crosslinks) to form microfibrils (strong fibres)

● Hydrogen bonds are strong in high numbers

● So provides strength to plant cell walls

Question 21

Describe the test for reducing sugars

Answer 21

1. Add Benedict’s solution (blue) to sample#
2. Heat in a boiling water bath
3. Positive result = green / yellow / orange / red precipitate

Question 22

Give examples of reducing sugars

Answer 22

Reducing sugars = monosaccharides, maltose, lactose

Question 23

Describe the test for non-reducing sugars

Answer 23

1. Do Benedict’s test (as above) and stays blue / negative
2. Heat in a boiling water bath with acid (to hydrolyse into reducing sugars)
3. Neutralise with alkali (eg. sodium bicarbonate)
4. Heat in a boiling water bath with Benedict’s solution
5. Positive result = green / yellow / orange / red precipitate

Question 24

Give an example of a non-reducing sugar

Answer 24

Non-reducing sugars = sucrose

Question 25

Suggest a method to measure the quantity of sugar in a solution

Answer 25

● Carry out Benedict’s test as above, then filter and dry precipitate ● Find mass / weight

Question 26

Suggest another method to measure the quantity of sugar in a solution

Answer 26

1. Make sugar solutions of known concentrations (eg. dilution series) 2. Heat a set volume of each sample with a set volume of Benedict’s solution for the same time 3. Use colorimeter to measure absorbance (of light) of each known concentration 4. Plot calibration curve - concentration on x axis, absorbance on y axis and draw line of best fit 5. Repeat Benedict’s test with unknown sample and measure absorbance 6. Read off calibration curve to find concentration associated with unknown sample’s absorbance

Question 27

Describe the biochemical test for starch

Answer 27

1. Add iodine dissolved in potassium iodide (orange / brown) and shake / stir 2. Positive result = blue-black

Question 28

Why do glycogen and starch act as energy stores?

Answer 28

Glycogen and starch act as energy stores because they are made of α-glucose, which is the substrate for respiration in cells. This produces ATP for energy release.

Question 29

Why is cellulose so strong?

Answer 29

Many hydrogen bonds